Tube Shields and Heat

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Tron Pesto, Dec 31, 2017.


  1. Tron Pesto

    Tron Pesto Member

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    Feb 18, 2016
    Do tube shields help dissipate tube heat or do they trap the heat?

    The reason I ask is I'm replacing some shot tube sockets on a 2 x EL84 franken-amp I built years ago. The tubes hang down and they've always run a little warm so I want to kill two birds with one stone: add support AND help dissipate heat.

    So:

    Shielded socket?

    or

    Retainer strap socket?

    What do you think?
     
  2. HotBluePlates

    HotBluePlates Member

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    It's cold out right now where I am. If I'm standing out in the cold, I sure like to have pants on that don't hug my skin as I stand. The little pocket of air between my legs & the pants keeps me warmer than if my legs were in close contact with my pants.

    So it is with tube shields. The kind often used is more for screening of electrical interference, as there is an air pocket between the tube & the body of the shield. Expect the tube will heat that air, and the shield will hold that hot air in & prevent as-effective cooling.

    There are different tube shields that were common in the old days: IERC shields.

    These have an anodized black (sometimes dark purple) outer sleeve that slides over a piece of metal with many small "fingers" which wraps around the tube. There is tight contact from that wrap-wound piece, the tube & the outer sleeve. These dissipate heat quite well. However, if you care about pristine labels on your NOS tubes, be ready... They will absolutely obliterate any printing on a tube due to the tight fit.

    IERC Shields in Use

    [​IMG]

    [​IMG]
     
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  3. Tron Pesto

    Tron Pesto Member

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    Thanks so much for that HBP! That makes sense. I just wasn't sure if maybe since metal conducts heat so much better than air, that the radiant heat the shields picked up was transferred to the chassis faster than the heat was "stored" in the air gap between the tube and the shield.

    So I'm going for retainer wire sockets, thanks again!
     
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  4. Avatar Tech

    Avatar Tech Member

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    Good call IMO. The power tubes should be orders of magnitude less susceptible to stray noise than preamp tubes.
     
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  5. TimmyP

    TimmyP Member

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    I've run across a few amps that required shields to keep them from oscillating at their highest usable gain settings, so it might be wise to at least put the shield bases on so you have the option.
     
  6. bluesky636

    bluesky636 Member

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    I use tube shields on the preamp tubes of all my amps without issues. A 12AX7 gets nowhere near as hot as a 6L6GC or similar power tube.
     
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